The auto-generated references are meant to be pithy, dense, and fast -- to be
references, not guides. The configuration reference was front-loaded with
several pages of explanatory text that properly belongs in the guides on the
docs site. This commit removes that text in preparation for a reorganization of
the docs.

This is a doc string only commit.

Inline documentation in lib/puppet/reference/configuration.rb stated that puppet agent accepted the
--mkusers flag, which is only intended for use with puppet master.

Individual metaparameters under the main H2 on the page should be H3s, not H4s.

Whits are inserted into the dependency graph in the place where an empty
class is being required. Unfortunately, when such a class is involved in
a loop, the error message shows the cycle as involving Whit[Classname].
This patch changes it to say Class[Classname], which is much easier to
understand. It also fixes puppetdoc from generating documentation on the
Whit type.